The present invention relates to a method for manufacturing a multi-layer composite by laminating a sheet-like element onto a backing in a laminating unit. The invention also relates to an arrangement for positioning a sheet-like element onto a backing, to manufacture a multi-layer composite in a laminating unit. The invention relates to a laminating unit for manufacturing a multi-layer composite embodying such a method and comprising such a positioning arrangement.
Multi-layer composite materials are used in the field of packaging, after they have been cut, folded and glued. One of these composites commonly used is corrugated board. It is used mainly as a protective packaging that is particularly strong while being readily recyclable.
Corrugated board is for example made up of an inner board provided with corrugations, bonded onto a first flat coverboard on one side of the corrugations. This inner board with first flat coverboard constitutes a single-face corrugated board. The single-face corrugated board obtained is also assembled by bonding with a second flat board on the other side of the corrugations.
To make the packaging more attractive, the corrugated board is often printed. This operation is performed by flexography in order to obtain quality prints in multiple colors. However, printed corrugated board may exhibit defects, for example in the case of relatively thin corrugated board. The defects are not acceptable for packaging for expensive products.
Some printing defects among others are lines corresponding to each crest of the corrugations because, during printing, the corrugated board will be crushed slightly. The difference in strength between the tops of the corrugations and the regions separating two consecutive corrugations is the main reason why these lines appear during the printing operation.
One technique then is to use laminating to assemble a sheet-like element in the form of a preprinted sheet of board, onto a backing in the form of a single-face corrugated board.
The sheet-like element is for example paper sheet, cardboard sheet, corrugated cardboard sheet or flexible plastic sheet, which is rough or printed, etc. The sheet-like element is already printed using flexography, photogravure or offset printing or converted using embossing, calendering or metallization by hot foil stamping, etc. The backing is for example paper board, cardboard, single-face corrugated board, double-face corrugated board or foam, etc.
To do this, a laminating unit comprises a section for feeding the sheet-like elements, the sheet-like elements being shingled, and a section for laminating the sheet-like elements onto the backings.
If the backings are in the form of boards, the laminating unit comprises also a section for feeding the backings. If the backing is in the form of a web, the laminating unit comprises also a section for cutting this web. The web comes from a reel or is produced in line upstream of the laminating unit.
In the laminating section, the sheet-like element is bonded by pressing between two rolls onto the backing that has previously been coated with glue.
In order to obtain a quality composite, the positioning of the sheet-like elements in the laminating section is an operation of key importance. The sheet-like element has to be positioned accurately so that later conversions are perfectly in register with the edges, printings, and/or conversions of the composite obtained.